cc ppt Transportation engg poly unit 4(4)

Poly unit 4.4

Transportation Engineering
- C. Coomarasamy
Formerly Professor / Director, JRPC Trichy.
4.4 Signaling:
Objects of signaling – Types – Classification according
to location – Special signals – Typical layouts –
Control of movement of trains – Following train
system – Absolute block system- Automatic signaling –
Pilot guard system – Centralised traffic control system.

4.4 Signaling
4.4.1. Objects of signaling
4.4.2. Types
4.4.3. Classification according to location
4.4.4. Special signals
4.4.5. Typical layouts
4.4.6. Control of movement of trains
(a) Following train system
(b) Absolute block system
(c) Automatic signaling
(d) Pilot guard system
(e) Centralized traffic control system.

4.4 Signaling

Definition:
Signaling consists of the systems, devices and means by which
trains are operated efficiently and tracks are used to
maximum extent, maintaining the safety of the
passengers, the staff and the rolling stock.
It includes the use and working of signals, points, block
instruments and other equipments.
Objects of Signaling:
1. To provide facilities for the efficient moving of trains.
2. To ensure safety between two or more trains which cross or
approach each other's path.
3. To provide facilities for the maximum utility of the track.
4. To provide facilities for safe and efficient shunting
operations.
5. To guide the trains movement during maintenance and the
repairs of the track.
6. To safeguard the trains at converging junctions and give
directional indications of diverging junctions.

4.4 Signaling

• Railway signaling is a system used to control railway traffic
safely, essentially to prevent trains from colliding.
• Being guided by fixed rails, trains are uniquely susceptible to
collision; furthermore, trains cannot stop quickly, and
frequently operate at speeds that do not enable them to stop
within sighting distance of the driver.
• The set of rules and the physical equipment used to accomplish
this determine what is known as the method of working (UK),
method of operation (US) or safe working (Aus.).
• Not all these methods require the use of physical signals and some
systems are specific to single track railways.
• The earliest rail cars were first hauled by horses or mules.
A mounted flagman on a horse preceded some early trains.
• Hand and arm signals were used to direct the “train drivers”.
• Foggy and poor-visibility conditions gave rise to flags and
lanterns. Wayside signaling dates back as far as 1832, and used
elevated flags or balls that could be seen from afar.

4.4 Signaling

A signal is
a mechanical or electrical device erected
beside a railway line to pass
information relating to the state of the line ahead to
train/engine drivers.
The driver interprets the signal's indication and acts accordingly.
Typically, a signal might inform the driver of the speed at which the
train may safely proceed or it may instruct the driver to stop.
Signals are used to indicate one or more of the following:
• that the line ahead is clear (free of any obstruction) or
blocked.
• that the driver has permission to proceed.
• that points (also called switch or turnout in the US) are
set correctly.
• which way points are set.

4.4 Signaling

• the speed the train may travel.
• the state of the next signal.
• that the train orders are to be picked up by the crew.
Signals can be placed:
• at the start of a section of track.
• on the approach to a movable item of infrastructure, such as
points/switches or a swingbridge.
• in advance of other signals.
• on the approach to a level crossing.
• at a switch or turnout.
• ahead of platforms or other places that trains are likely to be
stopped.
• at train order stations.

4.4 Signaling

'Running lines' are usually
continuously signalled.
Each line of a
double track railway is
normally signalled in
one direction only, with
all signals facing the
same direction on either line.
Where bi-directional' signalling is installed, signals face in
both directions on both tracks
(sometimes known as 'reversible working' where lines
are not normally used for bi-directional working).
Signals are generally not provided for
controlling movements within
sidings or
yard areas.

4.4 Signaling
4.4.2. Types
.

Operating
characteristics
1.Detonating signals
(Fog or audible
signals)
2.Hand signals
(Visual indication
signals)
3.Fixed signals
(Visual indication
signals)

Types of signals
Functional
characteristics
1.Stop or Semaphore
signals
2.Warner signals
3.Shunting signals
4.Coloured light
signals

can be classified into
various categories based on

Location
characteristics
1.Reception signals
(a) Outer signals
(b) Home signals
2.Departure signals
(a) Starter signals
(b) Advance starter
signals

Special
characteristics
1.Repeater or
Co-acting signals
2.Routing signals
3.Calling on signals
4.Point indicators
5.Modified lower
quadrant
Semaphore
signals
6.Miscellaneous
signals

Operating
characteristics

4.4 Signaling
4.4.2. Types

1.Detonating signals(Fog or audible signals)
2.Hand signals
(Visual indication signals) 2.Hand signals
3.Fixed signals(Visual indication signals) usually semaphore type,
fixed at a place . ( see next slide)
DANGER-STOP

1.Detonating signals
-fixed to rails by means of clips
-explode with a loud sound
-for safety
placed at least 400 to 500 m
ahead of signals

During day time
-by flags fixed to a wooden handle
-or by bare arms
CAUTION-MOVE SLOWLY
During night time
-by lamps movable glass slides
green- Proceed
red – Stop and
yellow- Proceed cautiously
Used by
guards,
Station masters,
Cabin man,
Gang man,
Key man,
Point man,
or authorised man

CLEAR-PROCEED.

in the case of a person riding
in or on a vehicle, either arm
waved up and down denotes

STOP.

Functional
characteristics

4.4 Signaling
4.4.2. Types

British semaphore stop signal
(lower quadrant type)

1.Stop or Semaphore signals (US - home signal or absolute signal)
2.Warner signals
Semaphore signals :
3.Shunting signals
-design is to show the stop position
of any failure that happens to be
4.Coloured light signals

Stop Signal – Danger

Ordinary position-horizontal- ie.,
ON position-indicates Stop or Danger
-when the signal is pulled- 45 to 60 deg.OFF-position indicates Proceed.

Stop Signal – Clear

Stop Signal Post

in the apparatus.
-in normal position- it indicates the
-stop position.
-placed on L.H.S of the direction of the
movement
-and the movable arm projects towards
-the track for indicating the signal.
-Semaphore: The semaphore arm of a
-stop signal is red in front with a
-white stripe near the end, and
-white in the back with a
-black stripe near the end.
-The arm is square-ended.
-Signal aspects are as shown.

4.4 Signaling
4.4.2. Types
A stop signal (US - home signal or absolute signal) is any signal --most
restrictive indication is 'danger' (which compels a stop).
Stop signals are used to protect junctions, points (US - 'switches'), level
crossings, movable bridges, platforms or block sections.
A particular signal box may control one or more stop signals on each
running line. In a traditional mechanically signalled area, have
two stop signals governing each line.
The first reached by a train is known as the home signal.
The last stop signal, known as the starting or section signal, is usually
located past the points etc. and controls entry to the block section ahead.
The distance between the home and starting signals is usually quite short
(typically a few hundred yards), and allows a train to wait for the section
ahead of it to clear without blocking the line all the way back to the
previous stop signal.
• At some locations, more than one home signal might be provided on
the same line.
• These will be identified by names such as
outer home and inner home, or first home, second home etc.

4.4 Signaling

1.Stop or Semaphore signals

4.4.2. Types

2.Warner signals
Semaphore Warner Signal
on a post by itself ('on').

Semaphore Warner Signal
on a post by itself ('off').

2.Warner signals: V notch at free end, and the white band is also V shape.
A semaphore signal
4.4 Signaling
at the entrance to
Station is combined
4.4.2. Types
with a warner signal.

Semaphore Warner signal in Two-4.Colour-light: The stop signal may have two (green above red),
three (green-yellow-red), or four lamps (yellow-green-yellow-red) .
Aspects are as shown below.

4.4 Signaling
3.Shunting signals

Ground Shunt Signal
- Danger

4.4.2. Types

Ground Shunt Signal
- Clear

Ground Shunt Signal
- Danger

Ground Shunt Signal
- Clear

Type - shall be either – (a) a Disc signal or (b)a Position light signal .
under special instructions ,a Shunt signal may be a miniature semaphore arm .
Disc Signals -The front of the disc shall be white with a red bar .
The back of the disc shall be white with a black bar .
By day, the bar of the disc shall be horizontal in the 'ON' position and 45 to 60 deg.
below the horizontal in the 'OFF' position in anti-clockwise direction .
By night the signal shall display red light in the 'ON ' position and
a green light in the 'OFF' position .
Miniature Semaphore Signal-( a ) The semaphore arm of the Shunt signal
shall be square ended. The front of the arm shall be red with a white bar .
The back of the arm, shall be white with a black bar.
The bars shall be parallel to the end of the arm.

4.4 Signaling
4.4.2. Types

Location
( a ) Shunt signal may be separately located on the post or close
to ground or may be fixed below a stop signal other than the
first stop signal of the station .
(b) Where shunt signal is required to be fitted on a signal post on
which a Calling-on signal is also fitted ,the shunt signal shall be
fitted below the Calling-on signal.
(c)A shunt signal; placed below a stop signal or a Calling-on signal shall
not be capable of being worked at the same time as the relative
stop signal or a Calling-on signal.
(d) Where a shunt signal is fixed below a stop signal it shall show
no light in the 'ON' position .
Diverging routes -More than one shunt signal may be placed on
the same post and when so placed ,the top most shunt signal shall
apply to the extreme left hand line and the second shunt
signal from the top shall apply to the next line from the left and
so on .One shunt signal with or without route indicator may
also be provided for a number of diverging routes.

Location
characteristics

4.4 Signaling

1.Reception signals; are the signals which control the reception
of trains into a station
(a) Outer signals (b) Home signals. At some stations, include
Routing signals.
(a)Outer signals
-is the first “stop” signal at a station, i.e.,
- indicates the entry of the train from block to station yard
- should be placed at adequate distance from the point up to
which the line can be obstructed after permission to approach
has already been given.
Adequate distance: In India, 0.54 km for B.G, 0.40 km for M.G
i.e., signals- provided at this distance beyond the station limit.
-generally one arm.
-but may have warner signal on the same post nearly 2m below it.
-The driver must bring his train to a stop at a distance of 90 m before
the outer signal and then proceed to the Home signal with
caution.

4.4 Signaling


(b) Home signals:
-Due to its location at door of station, it is termed as home signal.
-has bracketted arms to indicate which line is to be used.
-it is one of the important functions of interlocking to ensure that
the route is properly set before the signal arm is taken to
“OFF‟ position.
-So the function of Home signal is to protect the sidings already
occupied.
-is, therefore, located not more than 180 m from
the start of the points or switches and unless there are other
means of holding the route.
-lock retaining bars are provided to hold the route when the
distance is more than 180 m .
-hence signals carry as many arms as the
number of diverging lines.

4.4 Signaling


If, it is in „Proceed position‟ then the driver can take the train at
normal speed , assuming that Home signal is also in the
proceed position.
Two Aspect Signals- Outer Signal. :
1200 m in section where sectional speed is 100 km/ hour and above.
800 m where sectional speed is less than 100 km/ hour.
Where minimum visibility as above can not be achieved,
warner way be separated.
With the warner separated ,minimum visibility of outer shall be not
less than 400 meters.
Warner Signal on a post by itself
400 m
Home Signal
400 m
Main Starter Signals
400 m
All other Signals
200 m
Note : Where adequate visibility of stop signals cannot be provided,
repeater or co-acting signals shall be provided to ensure the
combined visibility or speed restrictions imposed.

4.4 Signaling


2.Departure signals are the signals which control the despatch of
trains from the stations . Types: (a) Starter signals
(b) Advance starter signals
(a) Starter signals:
- marks the limit up to which trains stopping at a station
come to a stand or halt.
- Home signals carry as many arms as the number of
diverging lines whereas separate starting signal is provided
for each line.
- The starter is the last stop signal at a station.
- If advance starter is not provided then is such cases, it has to be
placed outside all connections of the line to which it refers
unless permitted by approved instructions.

4.4 Signaling

- Thus, starter signal actually controls the movements of the
trains when they depart from the stations.
- No train can leave the station unless the starter signal shows
the “Proceed” position (i.e., inclined position)
(b) Advance starter signals:
-besides starter signal, an advance starter may also be provided
(generally 180 m or more) beyond the trailing points or switches.
-becomes the LAST STOP SIGNAL at the station where it is
provided.
-in general, it is an indication for the train having left the station and
-is no more the responsibility of the station master.

4.4 Signaling
4.4.5. Typical layouts

.

Positions of signals in Station-yard

DOWN movement

Outer signal

Advance
starter

Warner signal

185 m

185 m

640 m
Advance
starter

Outer signal

UP movement

Typical signal box layout

Warner signal

4.4 Signaling


• An advanced starting signal might be used at a location where it
might be desirable to advance a train from a station platform before
the section ahead becomes available.
• In this scenario, the starting signal permits the train to draw
forward from the station area toward the advanced starting
signal, which controls entry to the section ahead.
• If any of the signals beyond the first stop signal are at 'danger',
the previous signals will also be held at 'danger' until the train is
almost at a stand, to indicate to the driver that the next signal is at
'danger'.
• This can be enforced by instruction or by electrical interlocking,
which requires the provision of a track circuit on the approach to the
signal.
• In America, where the term home signal is in common usage, it
generally refers to the "generic"
• British definition of 'stop signal', namely any signal whose most
restrictive indication is 'danger'.

A Junction Signal

Approach, Route and
Track Locking

Signalling at a Double
Track Junction

Interlocking. In this case, the interlocking could allow Points
C4 to be set for the main line route and permit Signal C3 to
how a proceed aspect

Special
characteristics

4.4 Signaling

1.Repeater or Co-acting signals
2.Routing signals
3.Calling on signals
4.Point indicators
5.Modified lower quadrant Semaphore signals
6.Miscellaneous signals
Generally, when a train passes through a station without
stopping, the driver comes across the five signals in this
sequence.
WARNER,
OUTER,
HOME,
STARTER and
ADVANCE STARTER.

Special
characteristics

4.4 Signaling

But when the
driver‟s vision is obstructed by
(i) an over bridge between the signals , or,
(ii) sharp curvature in the alignment or
(iii) due to any other reason,
a signal is provided with
a duplicate arm of smaller size
at a suitable position which repeats the indication of
the signal ahead. It is therefore, termed as a
Repeater Signal. This signal is linked with the main signal and,
therefore, when the lever is pulled both signals are lowered
simultaneously.
As these signals work in unison with the main signal, it is called
“Co-acting Signal”.

4.4 Signaling

Special
characteristics


Semaphore Repeater Signal ('on').
Banner Repeater Signal ('on').

Banner Repeater Signal ('off').

Semaphore Repeater Signal ('off').

Special
characteristics

4.4 Signaling

2.Routing signals:
At big stations, where a
number of lines exist at the station
taking off different routes from the main line,
besides one main Home Signal,
Routing signals are provided at the
points of diversion.
Lowering of anyone of the signals
indicates the track for which the points are set.
The signal for main track (Home signal) is at
a higher level while signals for
other diversions are at a lower level.
Number of the platform or line- indicated by a number plate-e.g.,
1,2, 3 etc.

Special
characteristics

4.4 Signaling

3.Calling on signals:
-Consist of small arms below and parallel to Home Signal fixed on the
same vertical post.
-When a train stops with Home signal indication, then a
Calling on signal permits a train to proceed
cautiously by keeping this signal arm at “PROCEED” position.
- useful when repair works are going on.

Semaphore
Calling-on Signal ('on').

Lower Quadrant
Calling-on Signal ('off').

Upper Quadrant
Calling-on Signal ('off').

Special
characteristics

4.4 Signaling

4.Point indicators
-mainly used to indicate the route to driver
as a precaution against bursting of points
or running into occupied line when the
signals are not available for this purpose.
-do not indicate the correct setting of points,
-they should not be relied upon by the station
masters as a mean of verification of the
setting of points for movements in the facing
direction.
-consists of a rotating lamp-about its central
vertical axis.
-Lamp is enclosed within a box (four sides).
- points are set for the main track-white target
-Points are changed- rotates 90deg. green target
- (green disc or green light at night)

4.4 Signaling

Railway semaphore signal

Stop Signal – Clear

In rare circumstances, one can find
multiple signals placed on the same mast
one above the other; in such a case, the
convention is that the highest one refers
to the leftmost divergence, and successive
signals below it refer to successive routes
to the right.

Special
characteristics

4.4 Signaling

5.Modified lower quadrant Semaphore signals

- A distant signal placed at an adequate distance from the Home
signal.
- A Home and Warner signal combination is placed at an adequate
distance (185 m from the point)

Distant Signal
– Caution
Three-position Distant
Signal showing 'Proceed'
Three-position Distant
Signal showing 'Attention'

Distant Signal Post

Distant Signal – Clear

Combined signals: When owing to their location, it is necessary to
combine two signals, one stop signal only may be provided under
.
approved special instructions, capable of displaying any or all of the
following aspects:(a) Danger.
(b) Caution.
(c) Attention.
(d ) Clear.

Section Ahead Caution

Section Ahead Clear

Combined stop and distant signals
British semaphore stop and distant signals on common post (lower quadrant type)
Where signals are closely spaced, a stop signal and a distant signal can be mounted on
the same post. The distant signal is always the lower of the two. The two signals are
"slotted" so that the distant signal can only clear if the stop signal is clear. Both
signals display a light at night, which means that the 'danger' indication appears as
red over yellow.
Shunting and subsidiary signals
Shunting signals and subsidiary signals also exist in semaphore form, with smaller arms
and lights than are provided for main signals.
These signals may also take the form of a disc with a horizontal stripe which is rotated 45
degrees to the clear position.
Train order signals
It was common for train order signals to point the arm straight down to indicate
'proceed'.
Non-railway uses
Signals on the River Weaver Navigation, directing boats into the paired locks
Railway-style semaphore signals have been used to control movements of boats or ships
(e.g. at swing bridges) and also to control road traffic (e.g. at level crossings).

Sighting Board

Subsidiary Signal Subsidiary Signal Subsidiary Signal
Calling On
Shunt Ahead
Warning

Subsidiary Signals

Subsidiary Signal Danger

Subsidiary Signal Clear

A closer view of the down
inner home, as a train
enters the station.
In the distance
the double disc that
controls the exit
from the carriage
sidings can be seen.

Diverging Junction Signal Lesser Route

Diverging Junction Signal Main Route

This is the view in the opposite direction. The up advanced starter is cleared for a
departing train, and on the right is the down outer home. It is unusual for two successive
signals to have subsidiaries, but the one under the outer home is a warning signal which
can be cleared either if the incoming train is to be called on at the inner home, or to allow
the train to approach the latter if another train is leaving the station at the same time

Semaphore: The semaphore arm of a stop signal is red in front with a white stripe near
the end, and white in the back with a black stripe near the end. The arm is square-ended.
Signal aspects are as shown below.
Colour-light: The stop signal may have two (green above red), three (green-yellow-red),
or four lamps (yellow-green-yellow-red) as described above. Aspects are as shown below.

Screen Shot of
Signalling Layout Display
in Control Room

Route Selection

Route occupation display

Tracking the
•
.
movement of the train

The train has
released the points

Two trains are displayed

A second route is selected

The third train
arrives

Train 6460 moves
towards the siding

The third route is set up

Two routes freed for Up and Down trains to proceed

4.4 Signaling
(a) Following train system
(b) Absolute block system:
or (Space Interval system)
or (Lock and Block system)
(c) Automatic signaling
(e) Centralized traffic control system.

4.4 Signaling

One of the
basic objects of signaling is to
control the movements of trains with a view to
ensure safety by preventing accidents.
To achieve this goal , a particular system of working should be
adopted keeping in view three aspects.
• Safety
• Speed and
• Traffic density
The absolute block system is extensively used on the IR.
In the block system, the railway track is generally divided into
block sections.
A block system- distance between the last stop signal of one
block and the first stop signal of the block next in advance.
Automatic block system- distance between
consecutive stop signals.

4.4 Signaling

Various systems that work on one or the other railway for the control of
movements of trains are the following:
-“One engine only” system.
Initially only one engine-available-collision did not arise- one engine
–on the line-at a time.
-suitable for small sections where shuttle trains work with one
engine and one rake.
(a) “Following train” or “Train Interval” system:
• In this system, trains are worked between two stations by
dispatching them one after the other (all in the same direction)
• at specific intervals (generally at least 15 minutes).
• The trains are run at specific speeds (less than 25km/h).
• This ensures that there should only be one train in every 5km
stretch in the section between the stations.

4.4 Signaling

• The maximum number of trains simultaneously present in the
section is restricted to 4.
• Trains are dispatched only after the
station masters of both stations have been in
communication and have
agreed upon the number and timing of the trains.
• The driver of a train being dispatched in this system must carry
written authorization (Authority to Proceed, Following
Trains System) specifying the
destination, speed, and details of preceding and following
trains on the section.
• This system was introduced in many areas as an
emergency measure in 1941 in order to cater to the
urgent wartime needs of the railways in India.
• It is still used in some areas when there is a requirement for large
unidirectional movements of many freight trains
(also known as the Corridor System).

4.4 Signaling

(b) Absolute block system:or (Space Interval system) or
(Lock and Block system)
'Absolute Block' refers to a system where the track is considered to
consist of a series of sections, such that when
one train is occupying a section of track (the block section),
no other train is allowed to enter that section.
In addition, no train can enter an empty block section without
first securing the permission of the station in advance.
This is the most widely used system for ordinary train routes.
A station or signal box controls a block section in one direction
(from its rear),
and no train may enter that block in that direction
without permission from that signal box
(the station or signalbox is said to accept or receive the train). When
a train has been accepted,
no other trains can be accepted
on that block section until it has left that block section.

4.4 Signaling

• Obviously the
two signal boxes at
either end of the block section have to
tightly coordinate their actions,
• especially in the
case of block sections that
allow bidirectional movement on
a single line.
• The permission to enter the block may be in the form of a
physical token carried by
the train crew
while the train is in the block,
or may be implicit in the
aspects of signals governing
access to the block.

The section ahead was Absolute Block and through a tunnel

4.4 Signaling

(c) Automatic signaling or Automatic Block Signaling (ABS)
• the signals are automated and
operate in conjunction with track circuiting or other means
of detecting the presence of a train in a block section.
• When a train enters a block section,
the stop signal protecting that block
changes automatically to on or the Stop aspect.
• As the train moves ahead out of that block and
into the next block, the signal aspect
changes automatically to Caution.
• In multiple-aspect signaling, when the train is 2 blocks ahead
the aspect then changes to Attention, and then to Proceed when
the train has passed 3 blocks ahead.
• In 3-aspect signaling, the aspect changes to Proceed when the
train is 2 block sections ahead.
• In automatic block territory 2-aspect signaling is not used.

4.4 Signaling

• Each change of a signal to a
less restrictive indication requires
the train to have moved an
adequate distance in advance of the signal.
• The gray, white, or silver boxes marked
'LOC CAB' found by the side of the
tracks contain the circuitry to accomplish the
automatic signal transitions.
• Any number of
automatic block stop signals may be provided in
between two block stations; thus with this system,
the two stations
do not define the ends of a single block section as is usually
the case with manual absolute block working (excepting, of
course, the case of intermediate block sections).
• Minimally one automatic stop signal is provided
to the rear of a block station's first stop signal.

4.4 Signaling

One individual- Pilot guardaccompanies the train ( may also give written authority)- to the
station ahead and
returns after adequate time interval (15 minutes) to the
same station with another train.
Combines the principles of
one engine only and
Following train.
-used under specific occasions such as:
-A failure of block-telegraph or
telephone system in case of single line.
-In double line, when
one line is out of order and the
other line is to be used for up and down trains.

4.4 Signaling

(e) Centralized traffic control system:
• Centralized traffic control (CTC) is a form of
railway signalling that
originated in North America and
centralizes train routing decisions that were previously carried
out by
local signal operators or the train crews themselves.
• The system consists of a
centralized train dispatcher's office that controls
railroad interlockings and
traffic flows CTC territory.
• One hallmark of CTC is a graphical depiction of the railroad on
which the dispatcher can keep track of trains' locations
across the territory that the dispatcher controls.
• Larger railroads may have multiple dispatcher's offices and
even multiple dispatchers for each operating division.
• These are usually located near the busiest yards or stations and
their operational qualities can be compared to air traffic
towers.

controlled turnouts and signals utilizing computerized Centralized Traffic Control

Distant signals
A signal that provides advance warning of a stop signal ahead (and which does not
compel a stop when in its most restrictive position) is referred to as distant signal.
The term originated in the UK and is used throughout the English-speaking world. In
some regions, notably North America, the terms distant signal and approach
signal are both in common usage.
Because of the long distance required to bring a moving train to a stand, distant signals
must be located on the approach to the corresponding stop signal by at least the
braking distance of the worst braked train to use the route. This is particularly
important on high speed routes. At one time it was practice to take sighting distance
into account when positioning distant signals; the distant signal could therefore be
positioned at less than braking distance to the corresponding stop signal.
The driver of a train encountering a distant signal at 'caution' must expect the stop signal
to be at 'danger' and must adjust the train's speed so as to bring the train to a stand
before reaching it. The driver of a train encountering a distant signal in the 'clear'
position knows that all applicable stop signals controlled by the same signal box are
in the 'clear' position.
This is enforced by interlocking; the distant signal is prevented from assuming the 'clear'
position unless all relevant stop signals controlled by the signal box display 'clear'.

A Finish distant signal at the western approach to
Muhos station is displaying Expect Stop. In the background,
express train 81 is pulling away from the station

4.4 Signalling

End position detector

Decentralized point controller

cc ppt Transportation engg poly unit 4(4)

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cc ppt Transportation engg poly unit 4(4)